The present invention relates generally to stacker assemblies for use in document handling systems, and more particularly to a document stacker assembly having a novel variable pressure stacker plate.
Document handling or processing systems are generally known in which a plurality of documents, such as mailing envelopes and the like, are conveyed in serial upstanding on-edge relation from a feed magazine through one or more processing stations, and ultimately to one or more stacker stations after sorting. The stacker stations, alternatively termed stacker assemblies, receive the sorted documents in serial fashion and maintain them in upstanding on-edge stacked relation until removed for subsequent handling. See, for example, U.S. Pat. No. 4,955,596 which is incorporated herein by reference.
To maintain documents in upstanding stacked relation as they are fed into a stacker station, known stacker stations include vertically oriented stacker or pressure plates which engage the leading document in the stacker station and move progressively along the length of the stacker in response to successive documents fed into the stacker station. It is a common practice to apply a biasing force to the stacker or pressure plate so as to urge it against the stacked documents and maintain them in upstanding relation as the documents are fed into the stack from an in-feed conveyor or the like. If the stacker plate pressure is relatively light, thin documents, such as mailing envelopes on the order of 0.007 inch thick, can be readily introduced into the stacker. If the stacker plate pressure is too great, the thin mailing envelopes are prevented from readily entering the stacker and may jam at the entry into the stacker. If the stacker plate pressure is too light, heavier documents, such as mailing envelopes or flats up to 0.25 inch thick or greater, introduced into the stack at an early stage of stack buildup, may overcome the biasing force applied to the stacker plate and "kick" the plate rearwardly. This can result in the stacked documents falling to a substantially horizontal orientation with resultant malfunction of the stacker assembly. The present invention overcomes these problems by providing a stacker assembly having a stacker or pressure plate operative to support both lightweight and heavier documents fed into the stacker assembly.